1. Field of the Invention
This invention relates to a fuel metering control system for an internal combustion engine.
2. Description of the Prior Art
The PID control law is ordinarily used for fuel metering control for internal combustion engines. The control error between the desired value and the manipulated variable (control input) is multiplied by a P term (proportional term), an I term (integral term) and a D term (differential or derivative term) to obtain the feedback correction coefficient (feedback gain). In addition, it has recently been proposed to obtain the feedback correction coefficient by use of modern control theory or the like, as taught in Japanese Laid-Open Patent Application No. Hei 4(1992)-209,940.
Aside from the above, such a situation is frequently encountered. Namely, shortly after the acceleration pedal has once been released, fuel cutoff effected and open-loop control implemented, it often happens that the accelerator pedal is soon depressed again, causing the engine to accelerate and feedback control to be resumed. The feedback control is resumed after only a short time in this way, making it necessary to calculate the feedback correction coefficient once again.
When calculating the feedback correction coefficient using a control law such as an adaptive control law, the feedback correction coefficient, thus calculated, has high control response. However, it will take time for a controlled variable to become stable unless the correction coefficient upon returning to the feedback control is determined appropriately.
An object of the invention is therefore to provide a fuel metering control system for an internal combustion engine which determines the feedback correction coefficient appropriately at the time of returning from an open-loop control to feedback control such that the controlled variable becomes stable immediately.